A total of 60 premature infants who will be randomized to receive either a standard fortification regimen (n=30) or an adjustable fortification regimen (n=30). The adjustable fortification regimen encompasses increasing / decreasing the amount of fortifier and adding supplemental protein guided by periodic determinations of the protein concentration in human milk (PCHM), body weight and blood urea nitrogen (BUN). Growth rate, tolerance of enteral feeding, days to achieve 100kcal/kg/d through enteral feeding, length of parenteral nutrition and NICU stays will be measured and compared between groups.